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Elementary Science Education

Acids and Bases. What they are and how they work!

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      Bernard Nebel

      What is an Acid?

      An acid is any compound that will release hydrogen ions (H+) to the solution. Emphasize: a hydrogen ion is a hydrogen atom without its electron; it is effectively a proton by itself. How does this occur? In certain cases, a hydrogen atom is covalently bonded to another element in such a way that the hydrogen proton comes off leaving its electron behind. The proton is the hydrogen ion (H+); the other side, now with hydrogen’s electron, will be a negative (-) ion.

       Chemists make it easy to identify acids. In writing the chemical formula for  an acid, they put the hydrogen(s) that will become ions (free protons) at the front of the formula. For example: HCl, H2SO4, HNO3, H3PO4 are respectively hydrochloric, sulfuric, nitric and phosphoric acids respectively. In short, whenever you see an H at the beginning of the formula for an inorganic (non carbon) chemical, you can assume the compound is an acid. 

      In the case of organic (carbon containing) compounds, the acidic group is

      —COOH that designates a carbon with a double bond to one oxygen and another bond to an OH group. The H of this OH group tends to come off as a hydrogen ion (H+) (free proton) (acid) leaving the other side of the molecule as a negative ion. 

      Why/how does an acid attack a metal (or anything else)?

      Recall that a metal is metal atoms effectively in a sea of their surrounding electrons. Each free proton (H+) pulls an electron away from a metal atom converting it to the metal ion (metal +). The negative component (ion) of the acid now combines with the metal  + ion and takes it into solution. Every two hydrogens, now with an electron taken from the metal, join together (covalently bond) to form a molecule of hydrogen gas, which bubbles off.

      Fe     +      H2SO4      —->      H2      +      Fe++ +   SO4=

                    Iron         sulfuric acid            hydrogen         iron sulfate

                   Metal     2H+  + &  SO4=              gas               in solution

      The following video is a demonstration of this reaction but using magnesium (Mg) rather than iron and hydrochloric acid (HCl). Note that hydrochloric acid is contained in the deflated balloon. It is emptied into the flask containing water and powdered magnesium. The balloon is inflated by the hydrogen gas produced. The proof that it is hydrogen is demonstrated by igniting it at the end. Hydrogen is very flammable.



       General characteristics of acids—see text

      What is a base?

      A base is any compound that will donate hydroxyl ions (OH) to the solution. Emphasize: a hydroxyl group is an oxygen-hydrogen pair (ion) with an extra electron. How does this occur? Consider an ionically bonded compound such as sodium hydroxide, NaOH also known as lye or caustic soda. As it dissolves in water, each OH groups separates from its sodium atom taking one of sodium’s electrons with it. Thus, we have sodium ions (Na+) and hydroxyl ions (OH) in solution. Chemists enable you to recognize inorganic (non carbon) compounds,  by putting the OH at the end of the formula (see examples in text).

      Bases (OH ions) attack metals in a more complex manner than acids but produce much the same result. The metal atoms are broken away from the metal becoming ions and hydrogen gas is released. Below is the chemical formula for the reaction between aluminum (Al) and sodium hydroxide (NaOH) in water solution. Note that end products are hydrogen gas, which bubbles off, and the “salt” of the base and metal.

              2NaOH     +      2Al   +  2H2O     2NaAlO2     +   2H2

           Sodium hydroxide      aluminum.      Water         sodium aluminate       hydrogen

      Below is a fun video demonstrating the similar effect of a base and an acid attacking an aluminum can. 



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